The long-term objective of this project is to understand how the properties of excitatory synapses underlie information processing in local circuits in the visual cortex. We have established techniques for recording synaptic interactions among individual cortical neurons. It is proposed to perform dual recording from specific types of synaptically connected neurons. We should study excitatory connections among pyramidal neurons and excitatory connections between pyramidal neurons and inhibitory neurons. The results of our experiments will allow us to understand both the mechanism and function of excitatory interactions in local cortical circuits. Specifically, the aims of this proposal are: 1. What are the synaptic dynamics of unitary excitatory connections during prolonged activation? 2. What is the impact of activity of a single presynaptic pyramidal cell axon on the spiking of its postsynaptic target cell?